That will depend on your editor. Common ones I'm aware of are to highlight all the lines you care about, then either press Tab or Ctrl+]. Your editor might have something different instead though, so if you let us know what it is, or simply Google it for your editor, you can get a more specific answer.

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IDLE is very basic and can have issues if you execute your code from within the editor. BUT, it ships with Python, does the job and is easy to learn so there's no reason to dismiss it out of hand. Especially if your teachers and fellow students are using it. I often use it on my Raspberry Pi computers. I just use it for an editor and run my code from the command line. For any bigger projects I love the Pycharm 3 Free edition (but it has a learning curve all its own).

Cntl-] and Cntl-[ are the indent and un-indent shortcuts. TAB is actually the code completion function.

BTW, did it really not dawn on you to look in the EDIT and FORMAT menus before you posted this question??? Check it out, there are other shortcuts you may like.